Making the Short dual wire
Beverage better !
Jeff
VE1ZAC
It was always the
plan to bring both ends of the short Beverage into the shack and figure out how
to make this thing adjustable. Further, since you have two coax that are receiving
from two directions, it should be possible to make some sort of phase control
device and combiner which allows you to “Steer” these antennas.
Victor Misek to the rescue ! Victor has
written a book “The Beverage Antenna Handbook” , third
edition which provides the state of the art in practical Beverage construction
and use. Frankly, I found the information provided by the Antenna Handbook and
Low Band DXing to be interesting but frustratingly
incomplete. If you intend on building a short steerable Beverage, you want Victors book. You can
get it from Radio Ware at www.radiobooks.com Very obliging chap runs this little store.
Victor’s book is a self published job and gets out of stock. Charles at Radio
Ware chased Victor down and got some more copies. Thanks Radio Ware !
Victor calls these
shorter two wire antennas SWA’s, or Surface Wave Antennas. The traditional long and pointy Beverage are
known as COS , or Cone of Silence, antennas.
Here comes the radical
challenge to conventional wisdom: Victor claims that a SWA with a steerable null is
more use to the amateur than a field full of
Most of us have a
dream antenna setup consisting of a field full of long Beverage wires pointing
all directions. Unfortunately, most of us also live on small pieces of urban
land that preclude that dream from becoming a reality.
Read those two
paragraphs again and let it sink in. Could the best of both worlds be had with
a SWA and a steering device ? I now believe the answer is yes.
Victors book had very clear information on the
transformers for the feedpoint and reflecting end of the
SWA antenna. Yet again, I rewound my transformers and obtained better balance
from my antenna. But, the last step of my short Beverage quest was at hand. I
built one of the improved steering devices described in Vic’s book. Here is the
schematic for it (reprinted from Vic’s book):
And, here is my first version of the
device, shown in the following two collections of pictures. I thought I was
being clever with the packaging, but of course, things didn’t quite work out
the way I wanted. The next one will be about 50% of the effort of this MK1
version. This one includes a little sub box containing a port saver for the
Pro3 rig. I have since removed it and mounted it closer to the Beverage port on
the radio. My unit has 4 different phase shifter center frequencies that
coincide to the 3 bottom ham bands and one for the broadcast band. Three would probably be enough in the MK2
unit ( VE1RGB’s unit ?)
However, together
it went, and work it does !
Note
the little sub board on the back of the band switch making a neat collection of
my junk box coil and capacitor assembly. At this point, things look pretty
good. Then reality set in !
However, the unit
does what it was designed to do. The box was selected to sit near my right hand
just starboard of the radio. The weight in the bottom is to aid anchoring the
unit to the desk.
Inside got a
little ratty. The next one could be greatly simplified by using one board to
mount everything behind the controls. The board would be mounted to the
controls by lead extensions from the controls themselves. Much
easier and neater. I was trying to be too clever with this MK1 unit.
How does it work ?
WOW
! It works as advertised and then some. You can
literally steer a null around 360 degrees with this thing !.
Even in “
I suggest that
this device makes the short SWA set up at least three times more useful than it
was. Compared to a short single wire, I would say this is ten times more
effective. Bold claims, I know, but I think they are justified.
Rumour has it that DX Engineering is going to
offer a device like this to work with their commercial SWA parts.
The unit works by
taking one of the signals and running it through a plus and minus phase
shifter, and then subtracting the signal from the other signal via a hybrid
combiner transformer. The Fet gives a little help to the lossy part of the signal after going through the phase
shifter. There is also a control to provide an adjustable match to the other
signal… a real boon to the balance issue on these antennas.
If you hate noise.. you will love this setup. A
short two wire Beverage ,or SWA, and a null steering
device.